In wireless networking, an extended service set (ESS) is a set of two or more interconnected wireless basic service sets (BSSs) that share the same service set identification (SSID) and security credentials to appear as a single BSS to any station (STA) associated with one of those BSSs.
An overlapping basic service set (OBSS) is a common situation in wireless local area network (WLAN) deployments where two or more WLAN BSSs are established by independent entities (individuals, operators, etc.) in a close proximity within the interference range of one another. In an OBSS environment, access points (APs) typically do not collaborate with one another. A backhaul does not exist, so information is exchanged between competing APs over the air (OTA).